A disk-type dynamic filter assembly typically includes a housing which contains a filter unit comprising one or more filter elements and a rotary unit comprising one or more members. The filter elements of the filter unit and the members of the rotary unit may have any of a variety of suitable configurations. Very often, the filter unit comprises a stack of flat, disk-shaped filter elements while the rotary unit comprises a stack of flat rotary disks coupled to a shaft. The rotary disks are interleaved between the filter elements with a gap maintained between each filter element and rotary disk and the rotary disks are arranged to rotate with respect to the filter elements.
While the rotary disks are rotating, a process fluid is pumped into the housing through a process fluid inlet. The process fluid then passes through the gaps between the rotary disks and the filter element. Part of the process fluid, i.e., the permeate, passes through the filter elements and exits the housing through a permeate outlet. The remainder of the process fluid, i.e, the retentate, exits the housing through a retentate outlet.
The relative rotation of the rotary disks and the filter elements causes the process fluid in the gaps between the rotary disks and the filter elements to sweep the surface of the filter elements. Debris is thus prevented from accumulating on the surface of the filter elements and fouling or clogging of the filter elements is minimized. This extends the useful life of the filter elements.
While conventional disk-type dynamic filter assemblies have proven very effective, they nevertheless have several disadvantages. For example, although the useful life of the filter elements in a dynamic filter assembly may be extended, the filter elements will eventually become sufficiently fouled or clogged with debris to require removal. Unfortunately, removal of the filter elements can be exceedingly difficult. Conventional filter elements may comprise a portion of the housing itself and access to each of the filter elements may require complete disassembly of the entire dynamic filter assembly, including the filter unit and the rotational unit. Furthermore, mechanisms for attaching filter media to the filter elements further add to the complexity and intricacy of conventional dynamic assemblies. Because of the number of components of the attachment mechanisms and the fragility of the filter media, the integrity of these conventional dynamic filter assemblies may be initially questionable or may deteriorate very rapidly. Consequently, not only are integrity and integrity testing problematical, but removal and replacement of the filter elements are both technically difficult and time consuming.
Another disadvantage of conventional dynamic filter assemblies is that they are very difficult to clean in place, e.g., automatically clean without completely disassembling the assembly. A conventional dynamic assembly typically has a multi-component housing, filter unit, and rotational unit, each of which are rife with cracks and crevices. Further, the filter unit and the rotor unit are frequently constructed and positioned within the housing in a manner which results in stagnant regions or regions of low flow velocity within the housing. These cracks, crevices, stagnant regions, and low flow velocity regions all collect and harbor contaminants which are difficult or impossible to remove by cleaning in place.
Yet another disadvantage with conventional dynamic filter assemblies is that they heat the process fluid. The rotation of the disks within the housing causes the process fluid to heat up. Yet some process fluids are very sensitive to temperature. The heat transfered to the process fluid from the rotating disk can harm or valuable components of the fluid.
Further, to pump the process fluid through the dynamic filter assembly, conventional systems have employed a first pump for pumping the process fluid into the process fluid inlet and a second pump for withdrawing the retentate from the retentate outlet. While there are some applications in which the use of two pumps is advantageous, it nonetheless increases the cost and mechanical complexity of the dynamic filter system.